Recently, due to climate change caused by global warming and water contamination and environmental pollution caused by population growth and industrialization, there is a problem of water shortages increasing around the world. To solve the above water shortage problem, a variety of previous desalination technologies have been developed and used, and currently, a technology for reducing costs for producing fresh water is being actively developed.
Generally, sea water may have a total dissolved solids (TDS) concentration of 20,000 ppm to 50,000 ppm (mg/l). The TDS include a variety of monovalent, divalent and other multivalent salts or chemical species, and among them, sodium chloride accounts for 75 wt % of the total solids. Meanwhile, generally, drinking water has a TDS concentration of 500 ppm or less.
Conventional technologies of desalinating salt water may be classified into a physical treatment method such as an evaporation method, a reverse osmosis (RO) method, and the like and an electrochemical treatment method such as a capacitive deionization (CDI) method and electrodialysis. Also, in addition to using the desalination methods as a single process in a process, there is a hybrid desalination technology formed by combining a physical process and an electrochemical treatment method.
The evaporation method has advantages of a simple principle and apparatus and obtaining high-purity fresh water but a high energy cost is necessary. In the RO method, salt water is desalinated by using a principle of obtaining pure water from a solution when a pressure higher than osmotic pressure is applied. However, in the case of an RO desalination apparatus, generally, it is necessary to apply a higher pressure than osmotic pressure of salt water by using a high-pressure pump to desalinate the salt water. Accordingly, due to high power consumption of the high-pressure pump, energy costs are high. Also, since a pretreatment for protecting a reverse osmotic membrane which is very vulnerable to turbidity components and organic matter in water is very difficult, and a recovery rate of produced fresh water in comparison to raw water which flows into the apparatus is very low, fresh water production costs are actually high, so far.
Currently, the CDI among electrochemical treatment methods has been evaluated as a low energy-consuming desalination method. However, the CDI is applied on a small scale and is not yet commercialized on a large scale. Large scale commercialization thereof has been delayed because high capacity, flow paths, treated water quality, and the like thereof are unsatisfactory and the technology has not yet been developed to be adequate for treating high concentrations of salt water.
To overcome the above problems in a single process, a variety of hybrid desalination processes in which the evaporation method and the RO method are combined or the RO method and CDI method are combined have been developed. However, so far, there are still problems in which energy consumption is still high, high pretreatment costs are necessary, and a recovery rate is low.
The prior art related to the present invention is disclosed in Korean Patent Publication No. 10-1448017 (Oct. 8, 2014, titled Forward Osmosis Membranes and Method of Preparing the Same).